Directive antenna



' April 29, 1952 c. B. H. FELDMAN Y 2,594,409

DIRECTIVE ANTENNA Filed July 27, 1943 3 Sheets-Sheet 1 Has H64 #76.5

April 29, 1952 c. B. H..FEI DMAN 2,594,409

DIREQTINE ANTENNA Y INVENTOR C. B. H FELDMAN NcLE l v RECEIVING DIRECTIVE cHA AcrERIs-nc ron FIG. 4. ATT ORNE V April` 29, 1952 I c. B. H. FELDMAN DIRECTIVE ANTENNA 3 Sheets-Sheet 3 Filed July 27.,- 19in* M Y n... 4m MD T 59 FPUM TRANSLATION DEVICE FIG. /5

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O SCANNING SECTOR /N VEN TOR ANGLE '6 I7'. F ELDMAN ATTORNE V Patented pr. 29, i952 DIRECTIVE ANTENNA Carl B. H. Feldman, Rumson, N. J., assigner to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application July 27, 1943, Serial No. 496,325

This invention relates to directive antennas and particularly to centimetric directive antennas.

As is known, single unit and multiple unit directive antennas of the lobe switching and lobe sweeping types have been proposed for use in radar systems. Broadly considered, the prior art lobe sweeping antennas are of two kinds, the so-called mechanically steerable type and the socalled electrically steerable type. Ordinarily, in antenna systems oi the mechanically steerable type, the entire antenna, or a part thereof, is rotated or moved and, in the case of a multiple unit system, the physical spacing between units may be varied. Also, electrically steerable antennas as heretofore proposed are of the frequency variation and phase variation types. In the frequency variation antenna system, the operating frequency is ordinarily cyclically varied; and in the phase variation antenna system, the uniform phasing of the unit antenna currents is cyclically changed, for the purpose of producing the beam sweep. While the mechanically steerable and electrically steerable antennas,v mentioned above are satisfactory for certain purposes, and have been used with success, it now appears desirable to obtain a lobe sweeping antenna ofthe electrically steerable type which" possesses distinct advantages over the prior art lobe sweeping antennas. Moreover, it appears desirable to utilize, in `an antenna system of the electrically steerable type designed for operation at a substantially constant frequency, means comprising a minimum number of movable parts or elements for producing the lobe sweeping action. In accordance with the present invention, and as is explained more fully hereinafter, the lobe sweeping action is produced electrically vby velocity variation, that is, by varying thephase velocity of the waves delivered to or received from the antenna system.

It is one object of this invention to obtain highly directive microwave antenna.

It is another object oi this invention to vary the phase velocity characteristic of a dielectric channel.

It is another object of this invention to obtain a.' highly eiiicient lobe sweeping centimetric antenna.

It is another object of this invention to obtain a lobe sweeping antenna of compact construction and comprising a minimum number of movable parts.

It is anotherl object of this invention to steer Vor change the direction of maximum-action oi -a 11 Claims. (Cl. Z50-33.63)

single unit antenna or a multiple unit antenna, without moving the antenna, without changing the operating frequency and without employing a plurality of phase Shifters.

It is another object of this invention to produce, in an antenna system, lobe sweeping action over a scanning sector having its central direction perpendicular or broadside to the antenna or the array axis, by electrically steering the lobe without changing the operating fre quency and without utilizing phase changers.

It is still another object of this invention to steer or move the directive characteristic of an electrically steerable, substantially constant frequency, antenna system comprising a wave guide having spaced antenna apertures, without employing phase Shifters and without distorting the directive characteristic by second mode effects.

It is still another object of this invention to obtain, in a radar system comprising separate, closely adjacent transmitting and receiving antennas; a round trip characteristic having negligible minor lobes.

As used herein, the term phase velocity denoted by v is the apparent velocity of the wave along the transmission channel; and the terms velocity ratio and phase velocity characteristic, both denoted by lc, refer to the ratio of the phase velocity c in free space to the phase velocity v in the guide, the ratio being equal to the ratio .2 M where xa is the operating wavelength asmeasured in the air or ether and is designated herein the ether wavelength, and lg is the operating wavelength as measured in the dielectric guide and `is designated herein the guide wavelength.

utilizing H11 waves and the longitudinal antenna slot is located in an electric plane wall of the guide. The rotor extends longitudinally within the guide and is positioned adjacent the other electric plane wall or side. The rotor also contains a longitudinal slot and means are provided for continuously rotating the rotor. In operation, as the eccentric rotor revolves the phase velocity of the waves conveyed by the guide is cyclically varied, whereby the maximum direction of action of the slot or aperture antenna is oscillated through a desired azimuthal sector.

In accordance with a slightly different embodiment a so-called second kind leaky wave guide antenna of the type also disclosed in the aforementioned patent of G. C. Southworth and comprising an air-filled rectangular guide having a plurality of transverse antenna slots or circular antenna apertures in one magnetic plane wall, is equipped with a rotor of the type described above, the rotor being positioned closely adjacent to one of the electric plane walls. Each transverse or circular aperture has an individual or unit antenna directive characteristic and the several slots or apertures constitute a linear array having a space factor directive characteristic. Preferably, the distance between the adjacent apertures is such that, with the range of velocities obtainable with the selected rotor, the scanning sector may be positioned broadside. As in the embodiment first described above, the revolving rotor changes the phase velocity characteristic of the guide and, as a result, the space factor characteristic is cyclically oscillated across the major lobe of the unit characteristic. The dimensions of the rotor and of the rotor slot or aperture, are chosen so that a velocity variation range, dependent upon the spacing between the adjacent antenna apertures, is obtained which prevents the production of a second mode of lower velocity, and therefore prevents distortion of the space factor directive characteristic during its oscillation.

The invention will be more fully understood from a perusal of the following specication taken in conjunction with the drawing on which like reference characters denote elements of similar function and on which:

Figs. l and 2 are, respectively, perspective and transverse cross-sectional views of one embodiment of the invention;

Fig. 3 isa perspective view of the rotor used in the embodiment of Fig. l; and Figs. 4 and 5 are perspective view of rotors either of which may be used in place of therotor of Fig. 3;

Fig. 6 is a perspective View of a diierent embodiment of the invention; and Fig. 7 illustrates a measured receiving oscillatory directive characteristic for the embodiment of Fig. 6;

Figs. 8 and 9 are, respectively, a perspective view and a top view of a radar system in which the embodiment of Fig. 6 is utilized; ,and Fig. 10 illustrates the measured round trip directive characteristics for the radar system of Figs. 8 and 9;

Fig. v11 is a perspective View of another embodiment of the invention; and Fig. 12 is a directive diagram used in explaining the system of Fig. 11;

Fig. `13 is a perspective View of still another embodiment of the invention; and Figs. 14 and 15 are, respectively, a schematic diagram and a set of curves used in explaining the embodiment of Fig. 13.

Referring' to Figs. 1 Aand 2, referencenumeral' 4 I denotes a rectangular air-filled metallic waveguide comprising the fiat electric plane or a wall 2, the concave electric plane wall 3, the magnetic plane or b walls 4 and 5 and the enclosed air dielectric medium 6. Numeral 'I denotes a translation device, such as a transmitter, a receiver, or a radar transceiver, the device ,'I being connected to a coaxial line 8 comprising inner conductor 9 and outer conductor IIJ. The end portion II of inner conductor 9 extends through wall 5 and into the dielectric medium in a direction perpendicular to walls 4 and 5, whereby transverse electric or H11 waves represented by arrow I2 are emitted or collected by the exposed inner conductor portion I I. If device 'I is a transmitter the conductor portion II constitutes an exciter antenna element; and if device I is a receiver the conductor portion II constitutes a pick-up antenna element. The front electric plane wall 2 is in a vertical plane and contains a horizontal longitudinal antenna slot I3. Reference numeral I4, Figs. 1 and 3, denotes an eccentric, hollow cylindraceous or tubular rotor which extends longitudinally Within guide I and is p0- sitioned closely adjacent the rear guide Wall 3. The rotor I ll is supported near each end by the end walls I5 and contains a longitudinal slot or aperture I6. In one l-centimeter system tested the rotor diameter was about one inch and the slot width was about 312 of an inch. The rotor is connected through the drive shaft Il to a motor I8, the shaft preferably but not necessarily including an insulator I9. Y

Assuming that device 'I is a receiver and that member I4 is not rotating, the rotor angle 1p (Fig. 2) being equal to 90 degrees, the operation of the system of Figs. 1 and 2 will now be explained. Wavelets emitted at a distant station or reflected by distant targets are collected by the slot antenna I3 and conveyed as H11 Waves to the pickup element I I. The collected wavelets are then conveyed by line 8 to the receiver 7. The Wavelets received at any two discrete points therein as, for example, segmental antennas 20 and 2I, have a phase relation, as collected, dependent upon the direction 22 of the incoming wave. If the direction 23 of maximum action for the slot antenna I3 coincides With the wave direction 22, the wavelets arrive in phase at the receiver and a maximum receiving effect is obtained. The phase velocity o in guide I is such that, with rotor I4 stationary, the direction 23 of maximum action of the slot antenna I3 makes an acute angle with the normal to the plane of the slot I3 as, for example, the angle A=30 degrees, Where theangle or direction A=0 degrees is perpendicular'to the plane of the slot. With motor I8 actuated the rotor lli revolves and produces a variation in the phase velocity of guide I, and the maximum receiving lobe including the direction 23 of maximum action, is caused to oscillate in the azimuthal plane throughv a given angular sector or angle +0 to 0, Where 0:0 is the mean or central direction of antenna action in the sector.

The theory explaining the eiect produced on the phase velocity characteristic of the guide, by rotation of the eccentric rotor, is not fully understood. According to one theory, the change in phase velocity is caused by the cyclical variation of the cross-sectional area, and especially the transverse magnetic plane dimension b of the guide, since the frequency characteristic and the phase velocity characteristic are functions of the b dimension, as explained in the above-mentioned patent of G. C. Southworth. :This theory,

-gous manner, as explained in Patent 1,562,961, R. A. Heising, November 24, 1925;- vPatent 2,145,024, E. Bruce, January 24, 1939.(Fig. 1), yand Patent 2,236,393, A. C. Beck and H. T. Friis, March 25, 1941, the phase velocity of a conventional two-wire .line may be. increased by Iutilizing in the linea plurality of series capacitances or shunt inductances, and may be deycreased by utilizingshunt capacitances or series inductances. Most likely the velocity change in the guide I is a result of several interrelated factors.

Referring to Figs.4 4 and 5, numerals 24 and designate eccentric rotors either of which may be used in the embodiment of Fig. 1 in place of rotor I4. As illustrated, the velocity variator 24 is a solid metallic semicylindrical rotor having the flat surface 26; and the velocityvariator 25 is a solid cylindrical metallic rotorv containing a longitudinal slot 21. Other eccentric rotors may, of course, be utilized in the system of Fig. 1.

Referring to Fig. 6, vthe antenna comprises, as in Fig. 1 an air-,filled leaky wave guide I .of the rst kind having a longitudinal slot I3, an eccentric rotor I4 with a longitudinal aperture like aperture I6 of Fig. 1 anda motor I8 for driving the rotor. The guide .I is connected to the translation device 'I by coaxial line 8. Numerals 28 and 29 denote a pair of parallel metallic righttriangular shield membersspaced apart a dis- ,tance equal approximately to the a dimension of guide I. One edge 30 of member 28 is attached to the junction or linear corner formed by guide walls 2 and 4, and one edge 30 of member 29 is similarly attached tothe junction of guide walls 2 and 5, in a manner such that the shields 28,

29 constitute, in a sense, extensions of the b walls 4, 5 of Aguide I. Each member 28, 29l has an edge3l extending perpendicularly to the wall 2 and a hypotenuse edge 32, only that one pertaining to member 28 being labeled, extending perpendicularly to the mean wave direction 6:0 degrees. Since the direction 0:0 degrees corresponds to the mean phase velocity characteristic of guide I, edges 30 and 32 of each of members 23 and 29 form an acute' angle which is related to the mean phase velocity in guide l. Also, the aforementioned acute angle is equal to the acute angle A formed by the wave direction 0:0 degrees and plane perpendicular to the plane ,of slot I3. In one system constructed in accordance with Fig. 6, and tested, the above-mentioned acute angle was 30 degrees. Numeral 33 denotes a side shield member included between the edges 3l of members 28 and 29 and attached to the junction of side wall 2 and one of the end walls I5 of guide l. Thus, the arrangement or structure constitutes a harp antenna having a wide rectangular antenna aperture 34. Numerals 35 denote transverse anges or flared end pieces and numeral 36 designates side or longitudinal flanges. The anges 35 and 36 are attached to the four edges of the rectangular antenna aperture 34 and hence constitute a horn antenna.

In operation, Fig. 6, assuming device 1 is a re ceiver, pulsed centimetric waves are received, after reection from a distant target, by the wide antenna aperture 34 and guided by shield members 28, 29 and 33 to the narrow secondary antenna aperturel3 in guide I and are thence conveyed as Huwaves to device 1. As rotor I4'revolves' the phase velocity characteristic of guide I is cyclically varied and the direction'23 of maxi',- mum radio action is oscillated across the scanning sector bounded by the directions +0 and ''0. In other words, since c is a constant and 'u varies cyclically in accordance with the'variation in the rotor sloty angle ,l/ Fig'. 2the angle or direction 0 is cyclically varied. With the rotor :angle 1,1/ equal to 0 degrees, the highest'phase velocity v is obtained and with the rotor :angle 1;/ equal to 180 degrees the lowest phase-velocity xvv is' obtained. Y f f.

While the vertical plane of the slot I3 is angularly related to the azimuthal or horizontal scanning plane containing the direction 0 the rectangular antenna aperture 34 is included in the vertical Wave front plane which is perpendicular to the scanning plane. Thus, in a sense, the shield members. 28, 29 and 33 project the` slot antenna aperture I3 into the vertical wave front 'plane for the direction 0:0 degrees. Stated differently, the +0 and -0 scanning sectorfor more accurately the' mean direction 0:0 degrees, is, `relative to aperture 34, in the so-called broadside position. On the other hand, ,in the.;em' bodiment of Fig. 1, the azimuthal -scanning' sector is in the oblique position, that is, at an acute angle to thefantenna slot I3.:l In addition, the shields 28 and 29 function, in eiect, to change or transform vthe narrow antenna aperture I3 into la wide antenna aperture 34,* whereby the lobe Width inthe plane perpendicular to the scanning plane is decreased and the gain of the system is increased. As pointed out below, in the radar system of Figs. 8 and 9 the shields also prevent interaction'between thel separate transmitting and receiving antennas. The iiares 36 function as a horn and further decrease the lobe width in the plane perpendicular to the scanning plane.

The curves of Fig. 7 werev obtained during a receiving test of the system of Fig. 6. In Fig. 7 the lobe 31 shown in full line and Vhaving its principal "axis or direction 23 aligned with the 9: -7 degree direction, approximately,"corre spends tothe 12:0 position (Fig. 2,) of roten I4; and the lobe Q31 shown in dash line and aligned with the o: +3 degree direction, approximately, corresponds to the gl/:lSO-degree rotor position. During the test the velocity variator I4 functioned to oscillate direction 23 of the maximum lobe 3'! through the IO-degree sector bounded' by the -7 degree and +3 degree directions. -In this connection it is important to notev that lobe 3? is not switched from the full line to the dash line position but moves, back and forth, across the sector, as indicated on the drawing .by the two peaks of lobe 31 included between` the full line and dash line lobe positions.

Figs. 8 and 9 illustrate a radar system comprisinga transmitting harp antenna- 38 connected by line 8 to the transmitter 39 and av receiving harp antenna 40 connected by line Il` to the receive 4I. The harp receiving antenna 40 is the same as that illustrated by Fig. 6. The harp antennas 38 and 40 differ primarily in that the transmitting antenna 38 is not equipped with Ya velocity variation rotorand each right-angle shield member` 28, 29- has two l5-degree acute angles, whereas the receiving antenna 40 is equipped with a velocity variator I4 and each of the right-angle shieldmembers 28 and 29 has a 30-degree angle and a GO-degree angle. The guide I of the 45-degree antenna 38 has a wider b or magnetic plane dimension than guide, I of they 30-60 degree antenna 40, sincethe angle betweenthe slot I3 of antenna 38 and its direction of maximum action is 45 degrees whereas the angle between slot I3 of antenna 4i) and its directionl of maximum action is 60 degrees. Also, the rear guide wall of antenna 38 is flat, whereas the corresponding guide wall of antenna 40 is preferably made concave, as described previously, to accommodate the rotor I4. .The structures are superimposed so that their projected apertures 34 are included in the same vertical plane and their corresponding end flanges 35 are aligned. It will be observed 'that the transmission lines 8 are connected to the guides I near uncorrespondent ends of the guides so that the energies in the two guides I flow in opposing or diverging directions 42. Hence, considering the longitudinal axes of the two rectangular apertures 34 the directions of energy flow are exactly opposite, that is, the two antenna apertures havea reversed feed, as shown by arrows 43.

In operation, Figs. 8 and 9, pulsed centimetric waves are supplied over line 8 by transmitter 3S to antenna 38 andL maximum radiation occurs in a direction 44,corresponding to {iidegrees and perpendicularto the rectangularaperture 34. The stationary maximum transmitting lobe is sufficiently broadL to blanket or illuminate with radio energy theA desired azimuthal sector bounded by the angular directions -I-e and 0. Hence, pulses impinge upon all reflective objects disposed in the sector and are returned as echo waves to the receiving antenna 49. The motor-driven rotor I4 of the harp receiving antenna 40 causes themaximum lobe of the receiving antenna to oscillate and scan the +0 and -0 degree sector. More specifically, the maximum lobe, including the direction 23 of maximum action, of the receiving antenna 40', moves across the sector and the echo pulses are successively received, the receiver being preferably adjusted vso that the directional indication obf maximum lobe of the receiving antenna 48.

These primary lobes are established by the socalled "go waves in the guides I of antennas 38 and 40. In each of the guides I the return" waves, reflected by the end wall I5 remote from the coaxial line connection, establish a pronounced minor lobe at an angle to the axis of the slot vantenna I3 equal to the angle between the maximum lobe and the slot axis. In addition, in the case of each slot I3, one or more minor lobes having directions included between the maximum lobe and the slot axis are established by a component having a lower velocity mode. In Eig. reference numerals 4 5 and 45 .d.f. .ur.\t.e the principal; axes pf fthe pronounced umdesired reiiection lobes. and numerals 41y and 48 denote the principal axes of the undesired lower velocity lobes, respectively, for antennas 38 and 4G. The functional labels T, L and R refer to what has just been described as principal," lower Velocity and reflection," respectively. By utilizing a reversed feed for the two superimposed guides I of antennas 38 and 40, which antennas have their maximum lobe axes 23 and 44 superimposed or coincident, the lower velocity lobes 41 and 48 are displaced and in fact are established on opposite sides of axes 23, 44, so that they do not combine to form a pronounced round trip lower velocity lobe. As is known, the round trip directive characteristic for the system of Figs. 8 and 9 is the product of the receiving and transmitting characteristics, as expressed in terms of the square root of the power. Consideringl the reflection lobes and 4S, these lobes would not-align if the reversed feed were not used, since the antennas 38 and 4B have dissimilar angles. The reversed feed, however, insures the establishment of these lobes on opposite sides of directions 23, 44. Hence a highly desirable round trip characteristic having no pronounced minor lobes is obtained. The reversed feed necessitates, in part, orienting the two slots I3 at an angle, and the shields 28 and 29 function to prevent interaction between the angularly related slots. If antennas. 38 and 4I) had similar angles, and if the reversed feed were not used, it would be practical to include the slots I3 in the same vertical plane. In this case the shields 28 and 29 would not be necessary, and only horn flares, such as flares 36, would be required to prevent interaction.

Referring to Fig. 10 which illustrates the round trip directive characteristic for the radar system of Figs. 8 and 9, reference numerals 49, 50 and 5I denote the positions of the round trip lobe corresponding, respectively, to the rotor positions, Fig. 2. 0:0 degrees, Ila- 90 degrees and 5b=l80 degrees. The lobe position for the \l/=270 degrees is substantially the same as that obtained for the rotor position 1p=90 degrees. For the p0- sitions 50:0 degrees, 41:90 degrees and pr-180 degrees the lobe is aligned, respectively with the directions 6:-4 degrees, 0=0 degrees` and 0=|4 degrees. Hence, during the test, the lobe oscillated between the +4 degree and -4 degree directions. It will be noted that the round trip characteristic does not include pronounced minor lobes.

Referring to Fig. 11, reference numeral 52 denotes a leaky wave guide of the second kind having electric plane or a Walls 2 and 3, magnetic plane or b walls 4 and 5 and end walls I5. The front wall 4 contains a plurality of transverse antenna slots 53 each extending perpendicularly to the electric walls 2 and 3. IThe areas vof slots 53 are preferably tapered or graduated, as illustrated, for the purpose of equalizing the energies emitted or collected by the separate slots. The spacing between slots is ma where )la .is the ether wavelength and n is equal to or less than 0.5. The guide 52 is equipped with an eccentric longitudinalv rotor I4 which contains a longitudinal slot IE and is connected by a shaft II tothe motor I8. As in Fig. 1, the leaky guide 52 is Iconnected to translation device I by coaxial line 8 comprising inner conductor 9 and outer conductor I0. The exciter or pick-up I I extends into the guide in a direction such that H11 waves radiated or received have a polarization I2 perpendicularzto tbe-guide;wal1 4. ..It wm benotedthat the guideantennas of ,Figs.- 1, 6, 8. and 9. theA wave polarization` isl perpendicular tol the scanf.

ning plane whereas in the guide antenna of Fig. 11 (and Fig. 13) the wave polarization'is parallel to the scanning plane.

In operation, referring. to Figs. 11 and. 12 and assuming device 1 is a pulse transceiver, pulses are supplied by device .1 over .line 8 to guide 52,.,

and, foreach pulse, distinctwavelets are simu1..

taneously emitted by the rectangular aperturesv 53.-. Thepulses arereceived after reflection at a distant target and conveyed over line 8 to transceiver 1. The maximum directive lobe of each aperture antenna 53 is not sharp and in Fig. 12

is represented by the curve 54. During the ltrans-` mission and subsequent receptionA of the pulses, the motor driven rotor I4 causes the maximum space .factor lobe 55, FigL`12., Of the linear array comprising apertures '53 to move back' and forth across the. effective aperture lobe and therefore causes the resultant'or productlobe 56 to oscillate and scan the desired' angular lsector, 51. The rate of sweep or scan is determined by thespeed fof the rotor and the rotor speed andthe pulsing rate are preferably such that in transmission a large number of pulses are emitted 'during' each oscillationof the maximum resultant lobej56 The angle suming, as shown in Fig. 11, that the slots 53 are" spaced less than a half a wavelength, the direc-v tion of maximum action iswthe same asin the 'case of leaky -wave guides of the first kind andv no .significant secondary maxima should occur. It may be noted that if the slot spacing in structure of Fig. 11 were greater than. one wavelength, as in the system of Fig. 13 described below, the space factor characteristic would include two or more maximum lobes; and if it were greater than one-half wavelength. and less than one .wavelength the characteristic may include more thanv one maximum lobe..

Referring to Fig. 13, reference numeral 58 denotes a leaky wave guide ofthe second kind having in its lfront electric plane wall 4 the longitudinally spaced circular apertures 59, and numerals Gll designate end-on polystyrene antenna elements each ofwhich projects into, and is supported in, one of the apertures 59. The polystyrene elements or polyrods 6B are ofthetype disclosed in my v'copending application Serial No; 464,479, illed November 4, 1942, Patent No. 2,419,205 `issued April 2, 194'?, and the copending application of G. E. Mueller, Serial No. 469,284, filed December 11, 1942, Patent No. 2,425,336 issued August 12, 1947. As disclosed in the Mueller application the polyrods 60 are tapered for the purpose of securing a directive characteristic having a single maximum lobe of selected width and negligible minor lobes. As discussedv below the spacing between adjacent polyrods 60 is greater than one wavelength and preferably in the order of one and one-half to two wavei lengths, and the range of the phase velocity varatioor phase A velocitycharacteristic k must be such,.as explained below, that a phase velocity corresponding tofa second mode of the wave 'is not established in the guide, otherwise the space factor directive characteristic, corresponding to the desired operating frequency, of the linear array .comprising polyrods 60 would be greatly distorted. 'As discussed in Patent 2,129,669, A. E. Bowen, September 13, 1938, the wavelength in a rectangular air-filled guide conveying H11 Waves is controlled by the dimension b and the limiting condition for preventing the second mode is where M. is the ether wavelength.

The equation,` as given in the Bowen patent, expressingthe relation for Aa., b and )mis )dem where Xg is the guide'wavelengt'h, or

letting )5 2 1 t v (4) and substituting A@ for b, we have Jr (5) o.s65=k 7(5)' I-Ience,v asa rst limitation, the phase velocity rat-io or Ycharacteristic:

must be equal to or smaller than 0.865', asis indi--v cated by the horizontal broken line 6| in Fig. 15.

Referring .to Fig. 13, the -phase shift between adjacent apertures or polyrods is In order to get maximum radio action at any angle o, this phase shift must differ from 360 degrees by the quantity n--M 360 degrees "M Sinl From Equation 1l, for each direction 6 in a desired azimuthal sector and a givenvalue of n, the velocity characteristic lc may be determined. Referring to Fig. 15, the curves n=1, n=1.11, n=1.50, n=1.'15, n=1.90 and 11:2, .designated respectively by reference numerals 62, 63, 64, 65, 6B and 61, weredetermined in this manner. It will be observed that, for `a spacing of one wavelength (n=1) and a range of 0.5l to 0.865 for the velocity ratio-k; a scanning sector Aextending from +8` degreesA to. +30' degrees; as illustrated-by 'line E2', is obtained'without'second modek effects, the sector being centered approximately on the +19 degree direction denotedby reference numeral 68. With 1L=l, a second mode distortion is obtained for directions less thanj=8 degrees, since for theseV directions the value of; 1c exceeds 0.865. With n=2,` a 29 degree (i0'=l4.5' degrees)A scanning sectonextending; broadsidel and having its mean direction perpendicular to the plane of the polyrods 60 may be secured by dimensioning the velocity variator I4 so that lc varies over the range 0.23 approximately to 0.76 approximately, Inaccordancewitlr the invention, the,4 dimensions of the variator` Ill andespecially of, the variator slot I6 are selected to give the proper velocity variation for a given constant operating frequency, a given value of .n and a given desired angular scanning sector i0, preferably but not necessarily, centered on the :0 direction. In this connection, itl may be noted that the proper width of slot I6 in rotor" I4, Fig. 3, or the proper width and proper depth of'slot'21 in rotor 25 of Fig. 5, for securing a desired variation in Ic, may be easily determined experimentally, inasmuch as rotor I4 Without the slot I6 or rotor Z1 Without the slot 21 produces no velocity variation.

The operation of the system of Fig. 13 is believed to be apparentiinviewfof tl'iedescription given above relative to' Fig. 11. Briefly, pulses are supplied by`device` 1 over linel 8r to guide 58 and, for each pulse, distinct wavelets are simultaneously emittedl by thepol'yrod's 6G; Assuming n=2, during the transmission and subsequent reception of the pulses, the motor driven rotor I4 causes the primary space factor lobe to oscillate across the 29 degree sector, Fig. l5, and across thev major lobe of eachv polyrod 50. As shownby thedash-dot lines'69 and 10, Fig. 15, which traverseY the lines 65, 66 andA 61,' withthe primary maximum lobe atv one extremity of the scanning sector, a secondary, maximum lobe occurs at the other extremity. Thus for n=2, assuming the primary lobe is moving from the 0:0 direction to` the-l'degree direction, a secondary maximum lobe appearsv at' the +15de'- gree as the primary lobe reaches the degree direction. As disclosed in my copending application, mentioned above, the minor lobes of the directive characteristic of each polyrod 65 should have negligible intensities; and the shape of the polyrod major lobe should be such that, during the scanning, only one maximum space factor or array lobe intercepts at any given instant the polyrod major lobe whereby unambiguous scanning is secured.

Although the invention has been explained in connection with certain embodiments, it should be understood that it is not to be limited to the embodiments described, inasmuch as other apparatus may be satisfactorily employed in practicing the invention.

What is claimed is:

l. In combination, a metallic rectangular Wave guide, means for supplying to or receiving from said guide transverse electric centimetric Waves polarized perpendicularly to one pair ofV Wave guide walls, a plurality of antenna apertures spaced along a longitudinal dimension of one of said. Wallsv and' constitutinga linear antenna array, and means extending longitudinally Within said guide for changing the distributed impedance of said guide whereby the phase'velocity of the waves conveyed in said guide is varied and 12 the space: factor` directive characteristic; of saidv array; is' movedA relative to saldlongitudinal dimension.

2. In combination, a wave guide having atleast one metallic Wall, meansforl supplying toorreceiving'from said guide centimetric'waves', polarized perpendicularly to said wall, a linear antenna array comprising a4 pluralityof parallel rectangular slotsY or apertures spaced along a longitudinal' dimension of saidA wall.. and'v means extending longitudinally within said' guide for Varyingthe phase velocity of" the waves in said guide.

3. In combination, av radio translationl device,

' a. wave guideA connected thereto and having inA one, wall. aplurality of unit antennas spaced longitudinally, means, for. impressing on; said Wave guide.- a Wave4 of a substantially constant freduency, .andi independent means .'for.: varying; thel phase. velocity characteristic, of.' said; guide overh a` range related' to v said. spacing.

4.. InV combination, a. radio translation; device, a` wave. guide connected thereto` and havingV in one vWallaplurality, of unit. antennas spaced' longitudinally, means for` impressing. onsaidr wave guide a. wavev of. a substantially constant frequency, and independent means for varying the phase velocity characteristic over a range related to said spacing and including a mean value corresponding to a wave direction perpendicular'to said wall.

5; In combination, a radio' translation device, av rectangular Wavev guide connected thereto'- and having in onev wall a plurality ofl antenna apertures spaced longitudinally; means` for impressing onv saidwavel guide a wave of a substantially constant frequency, and' independent; means for varyingthek phase velocity-characteristick over a rangel related to said' spacing', one value in said range corresponding; to a wave direction perpendicular to ,said Wall and each value in said'rangc being-smaller than 0.865,.

6.' In combinatioma` radio transceiver, a wave guide Vconnected thereto andhaving inr one wall a plurality of antenna apertures spaced along a longitudinal wall dimension, thespacng'between apertures beingI greaterV than `one-half the operating ether wavelength, means for impressing on saidv Wave guide a Wave of a substantially constant frequency, and independent' means for varyingthe, guide phase velocity over a range related to saidspacing and including a value corresponding to broadsde ratio action.

'7. Incombination, a Wave guidehaving` at least one metallicv wall, means for Supplying to or receivingfrom said guide centimetric waves, alinear antenna array comprising` av plurality of graded circular apertures spaced alongl aA longitudinal dimension of said guide Wall, and having individual directive lobes, and means extending longitudinally within said guide for cyclically varying the phase velocity of the` Waves in said guide, whereby the maximumV lobe of the space factor directive-characteristic is cyclically moved across theI individual lobes.

8. In. combination.. a rectangular Wave; guide having a: longitudinal slot in a first side Wall for 'directionally receiving centimetric Waves, a receiver connected thereto for'utilizing a transverse electric Wave component of. said waves polarized perpendicularly to said wall, means Within said guide for-cyclically varying the phase velocity of said` components, and a pair of triangular metallic shield membersv extending from the linear 13 junctions of said rst Wall and the adjacent guide Walls in directions parallel to said adjacent walls,

one edge or border or each shield member being perpendicular to said rst wall and another edge or border being perpendicular to the mean wave direction.

9. In combination, a transmitting antenna comprising a first rectangular wave guide having a. longitudinal slot in one wall for directionally radiating centimetric waves and a first pair of parallel triangular shield members attached to said wall, a receiving antenna comprising a second rectangular Wave guide having in one Wall a longitudinal slot for directionally receiving'said wave after renection from a distant surface and a second pair of parallel triangular metallic shield members attached to the last-mentioned Wall, the longest edges or sides of said four shield members being included in the same plane, a transmitter connected to the rst guide and a receiver connected to the second guide, means included in the second guide for cyclically varying the phase velocity of the received components.

10. In combination, a metallic rectangular 1airlled wave guide, a centimetric transceiver connected therewith, one of the guide walls having a longitudinal antenna slot, an eccentric member comprising a cylindrical air-lled metallic rotor having a longitudinal slot, extending lon- 14 gitudinally within said guide and facing the rstmentioned guide wall, and means for continuously rotating said member.

11. In combination, a metallic rectangular airlled wave guide, a centimetrc transceiver connected therewith, one of the guide Walls having a longitudinal antenna slot, an eccentric member comprising a cylindrical solid metallic rotor having a longitudinal slot, extending longitudinally within said guide and facing the first-mentioned guide wall, and means for continuously rotating said member.

CARL B. H. FELDMAN.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS 

